The present invention relates to the field of sampling of gaseous fluids and more particularly to the sampling of aldehydes and ketones contained in gases such as exhaust gases of internal-combustion engines. Any gas discharged by thermal combustion engines and containing notably aldehydes and ketones can be sampled according to the invention.
A particular application of the invention relates to the sampling of aldehydes and ketones, non-regulated specific pollutants, discharged in the exhaust gases of automobile engines installed in test cells for example.
Known sampling methods mainly consist in diluting the aforementioned gases, then in passing them on a particular solid adsorbent that traps the carbonyl compounds. The chemical trap is treated later in a laboratory where it is analysed in order to quantify individually each pollutant.
Concerning the measurement of aldehydes and ketones in the exhaust gases of cars, most analysis laboratories use either a sampling technique by exhaust gas bubbling in a suitable liquid derivation solution (acetonitrile as the solvent), or a Dinitro-phenylhydrazine-grafted silica cartridge allowing to withdraw and to chemically derive these hydrocarbon-containing species into hydrazone compounds. The grafted cartridge must thereafter be subjected to a treatment in the analysis laboratory that allows these compounds to be brought into solution in a solvent (acetonitrile). The latter sampling and measurement technique has the advantage of being more effective, easy to use and it offers possibilities of medium-term storage of the samples. The hydrazone derivatives obtained by either sampling technique are then separated by injecting an aliquot of this solution into an HPLC (High-Performance Liquid Chromatography) unit and detected individually by UV absorption.
Each laboratory adapts with its own available measuring material and works without interactive connection between the various elements around the sampling support, and without any really reliable, accurate and reproducible sampling protocol.
The present invention allows the use of commercially available cartridges, fast and sealed setting in a sampling support, simple programming of the sampling parameters, complete sampling automaticity when orders to start trapping of the effluents are given. It provides permanent control of the sampling conditions during the sampling cycle (flow rates, temperatures, pressure drops, sampling time . . . ), immediate alarm in case of malfunction or of failure to respect a procedure.
Furthermore, the present invention eliminates any risk of pollution of the sampling cartridge after it has been installed in its sampling support.
The object of the present invention thus is a unit for sampling aldehydes and ketones contained in previously diluted exhaust gases from thermal combustion engines, comprising an aldehyde and ketone trapping circuit and associated control means.
According to the invention, the unit further comprises:
a circuit for simulating the passage of the gases into the trapping circuit, arranged parallel to the trapping circuit,
a means for passing the diluted exhaust gases into either the trapping circuit or the simulation circuit,
a temperature detector upstream from the trapping means,
a pressure detector downstream from both circuits,
a mass flow regulator,
a means for circulating the gases, such as a pump.
More particularly, the trapping circuit comprises a specific cartridge arranged in series with the temperature detector.
Furthermore, the simulation circuit comprises a filter arranged in series with a throttling means.
The means for selectively diverting the diluted gases towards the trapping circuit or the simulation circuit specifically comprises two three-way solenoid valves situated respectively upstream and downstream from the two parallel circuits.
Furthermore, the unit according to the invention can comprise a means for diluting the exhaust gases.
The dilution means itself can advantageously comprise a dilution probe having an inlet for the gases withdrawn and an outlet connected to the inlet of the sampling circuit, and a microtunnel that cooperates with said probe.
Besides, said microtunnel comprises an outlet connected to the inlet of the dilution probe through a connection for dilution air, the inlet of the microtunnel receiving part of the diluted gases coming from the dilution probe.
Without departing from the scope of the invention, the unit further comprises a detection and alarm means in case of a malfunction of one of its elements.
The present invention further relates to a process for sampling aldehydes and ketones contained in diluted exhaust gases from thermal combustion engines, consisting in trapping said aldehydes and ketones in a specific circuit.
The process according to the invention further consists in passing the diluted gases for some time into a simulation circuit before they are passed into the trapping circuit, the two circuits being arranged in parallel.
According to the invention, the temperature of the gases is controlled in the trapping circuit.
Furthermore, the pressure of the gases is controlled downstream from the simulation circuit and the trapping circuit.
Besides, the gases are passed into the trapping circuit when the composition of the gases is considered sufficiently representative.